The spreading and sealing of epithelial sheets is an essential process during early animal development. Failure of epithelial sheet sealing has important implications for common birth defects, including spina bifida and cleft palate, and misregulation of proteins involved in this process is implicated in many types of cancer. The C. elegans epidermis is a powerful model system in which to study the dynamics of epithelial sheet sealing. Our previous studies have shown that two multiprotein complexes must be dynamically recruited to nascent cell-cell contacts during epithelial sheet sealing: the cadherin/catenin and SAP97/Dlg complexes. A key issue to resolve regarding cadherin/catenin function is how alpha catenin recruits and connects to the actin cytoskeleton. A key issue to resolve regarding SAP97 family proteins is how they are recruited to the membrane and how they form stable complexes once there. We will use a powerful combination of genetics, innovative in vivo imaging, and novel in vitro approaches to address these issues. First, we will determine the role of HMP-1/alpha-catenin in stimulating polymerization of and attachment to F-actin during morphogenesis, using in vitro assays, genetics, and in vivo imaging. Second, we will determine the role of unc-34/Enabled in stimulating recruitment of F-actin during morphogenesis, and we will identify new genetic modifiers of alpha-catenin function. Third, we will determine the role of domains of DLG-1/SAP97 in assembly of a multiprotein complex during morphogenesis, and we will analyze candidate DLG-1 interacting proteins. Fourth, we will determine the role of the DLG-1 binding partner, AJM-1, in stabilizing the DLG complex during morphogenesis, using biochemical assays, 4d multichannel imaging, and FRET. As a result of these studies, we will clarify how the cadherin/catenin complex recruits the actin cytoskeleton, and how the SAP97/Dlg complex is recruited and stabilized at nascent cell-cell contacts during epithelial sheet sealing. Because these studies will be carried out in a living organism, we will gain fundamental new insights into how these key junctional complexes regulate a fundamental morphogenetic event. [unreadable] [unreadable]